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    <title>Document</title>
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<body>
    <h1>我是b页面</h1>
    <button>退回主页</button>
    <button>退回上一个历史记录</button>
    <script>
        var btn = document.getElementsByTagName("button");
        btn[0].onclick = function() {
            window.history.go(-2);
        };
        btn[1].onclick = function() {
            window.history.back();
        };
    </script>
</body>

</html>